Shirttail hardfacing



1954 A. E. WISLER ETAL SHIRTTAIL HARDFACING Filed March 15, 1962 TEETH 1SHANK m i LC w m l v 5m WL m LT AS E s R U m U D P m U 0 F mum m GE m GWE NCL B QM T ADE RW M R 1 A Z MHZ B32 2 2 03m 125 M 022910 wmom m 252ad; .2

TORNEY United States Patent 3,158,214 SZERTTAIL HARBFAQKN'G Allen E.Wisler and Stanley R. Scales, Houston, 'li'ex., assignors to Hughes Toolilornpany, Houston, Tex, a corporation of fielaware Filed Mar. 15, 1362,Ser. No. 179,557 9 Claims. (Ci. 175-375) The present invention relatesto hardfacing structures on earth penetrating tools, particularly on theouter surfaces of the bit legs of rolling cone rock bits. Such surfacesextend to full gage or only slightly less, and are consequently exposedto considerable abrasive Wear. In mud drilling, such exposure ordinarilyproduces no very marked amount of wear, and the bit legs consist ofalloy steels which are hardened by heat treating but usually have nohardfacing on their outer surfaces. However, in the more recentlyintroduced and now often used air and mist drilling techniques,aggravated erosive wear on such surfaces does result from drillinthrough certain types of hard formations, e.g., those containingsiliceous material.

The observed Wear may take place over most of the outer surface of thebit leg, and has heretofore been anticipated and minimized in a numberof ways. Since one result was wear of the now commonly used weld metalused to retain the ball plug in position, hardfacing has been addedaround the weld metal plu This hardfacing has typically been in areverse .5 pattern, i.e., a band of welded hardfacing having a verticalleg between the ball plug weld metal and the leading edge of the leg anda generally horizontal leg between the weld metal and the tip of theshirttail (lower end) of the leg. In Hugheset, type bits, i.e., thoseusing cylindrical compacts or inserts of a hard material such astungsten carbide in place of the more conventional steel cutting teeth,similar compacts with flat outer ends are ofen used to protect the weldmetal, most often in a U pattern wherein the cross-arm is disposed inthe shirt-tail and the compacts in one vertical leg lie betwee thecompacts in the other vertical leg so that no nar ow horizontal band isleft unprotected. This structure has also been modified by usingshallower holes than those used to retain compacts and welding tubehardfacingin such holes.

While such harufacing str ctures have proven adequate to protect theweld plug and he niaior partof the bit leg surface from erosion, thehave not successfully cornbated erosion of the shirttail at d the areaabove the shirttail and below the ball plug weld. This area isparticularly important because it constitutes one side of a fairly sharpcorner, the other side of which is defined by a machined annular surfacesurrounding the bearing pin or" the bit leg. The latter surface servesto retain a set of rollers in place, and it wi l be apparent from theaccompanying drawing that erosion of the sharp corner will expose suchrollers and ultimately cause them to fall out and prevent normalfunctioning of the rolling cone.

This result has indeed obtained on occasion and is undesirable forseveral reasons. lthough the cutting structure of the bit is often stillrelatively sharp, drilling must be halted while repairs or replacementsare made. A cone left in the hole will interfere with subsequentdrilling, and may have to be removed with fishing tools. In deep welldrilling, the cost of a premature round trip to replace the bit, withthe time-consuming and costly raising, uncoupling and stacking of drillstem sections (and reverse in putting the new bit on bottom) far exceedsthe cost of hardfacing necessary to insure bit leg protection.

In approaching the present invention of furnishing hard facing extendingto the lower tip of a shirttail, the present inventor first triedextending the reverse J hardiacing mentioned above to a point /2" abovethe tip of the shirt- 3,158,2l4 Patented Nov. '24, 1%64 tail. When thiscaused some improvement in abrasion resistance but still permittedpremature erosion and loss of rollers, the gap between shirttail tip andhardfacing was reduced to /2". Despite the narrowness of this gap, therewas only a slight increase in performance, excessive wear of theunprotected metal in the gap and loss of rollers still taking placebefore full dul-ling of the cone cutting structure.

It appeared to be necessary to extend the hardfacing all the Way downthe shirttail, but this created obvious problems. The metal at theshirttail tip is so thin that there is Very little back-up material tosupport the relatively brittle hardfacing. In addition, it was knownfrom prior experience that hardfacing extending to the very edge of asurface and exposed to the type of abrasion here involved (continuousgrinding) would be quickly undermined and washed out.

The essence of the present invention lies in providing a very narrowhead of hard, tough metal adjacent the periphcry of the shirttail andproviding hardfacing extending upwardly from the upper surface of suchhard, tough metal head. The metal bead may be of any of a number ofcompositions of reasonable toughness and having an in situ hardness of25 to 35 Rockwell C, or any greater hardness which may be achievedWithout sacrifice in toughness. Suitable met s, hardfacing materials andtechniques are described below in the example To better understand andappreciate the present invention, this application includes a drawing inwhich:

FIGURE 1 is an elevation of a three-cone rock'bit in inverted position,looking directly at one of the bit leg outer surfaces here involved, and

FEGURE 2 is a partial vertical section looking in the direction of thearrows marked 2-2 in FIGURE 1 1'0- tated clockwise.

Fl'GURE 1 shows in inverted position a conventional three-cone rotarybit comprising the threaded and tapered shank ll integrally extendingfrom head 2, three bit legs 3 integral with the head extending in theopposite direction, and three rolling cones 4 mounted on bearing pins 5of bit legs 3 extending inwardly toward the bit axis and axially awayfrom shank 1. Steel teeth 6 are illustrated, though it is believed to beapparent that the present invention may be used with any type cuttingstructure and with bits or reamers, etc., having any number of rollingcutters. H

As may be seen from FIGURE 2, the now commonly used cone mountingstructure includes rollers 7 and balls 3 mounted in appropriate spacesbetween cone 4 and bearing pin 5. Cone 4 is mounted on pin 5 withrollers '7 in place, after which balls 8 are loaded through bore 9 fromits opening it) in the outer surface of bit leg 3. When all of the ballsllnecessary to fill the ball race definedby cone l and bearing pin 5have, been added, bzdl plug 11 is inserted to prevent the escape of anyballs, thus locking cone 4 to the bit. Movement of plug 11 is preventedby welding it to hit leg 3 with weld metal 12. The shirttail of bit leg3 is indicated by the numeral 13, and is generally regarded as thatportion lying between tip 14 and the dashed line 15.

The material added to the above described structure by the presentinvention is indicated by metal bead 21 and hardfac ing 22. Metal head21 extends from shirttail or hit leg-tip l4 and need be of onlyrelatively smdl thickness and width. Hardfacing 22 consists of particles23 of a hard metal such astungsten carbide dispersed'in a suit-v ablebinder 24. Both materials are applied to bit leg 3 by a variety of wellknown welding methods, depending on the state of assembly ofthe bit.[Whenthe bit has been completely assembled with cones, fbearings, ballplug, etc, or when an unassembled third of a bit head has already beenheat treated, metal arc welding methods are preferred because relativelylittle heat is dissipated throughout the bit, while if the hardfacing isdone prior to the heat treatment of the unassembled bit third thegreater heat of an atomic hydrogen torch can be tolerated. (A bit thirdincludes a bit leg 3 with bearing pin and a /3 portion of head 2 andshank 1, three such thirds being welded together in forming a Tri-Conerock bit.)

The complete hardfacing shown in FIGURE 1 is in the aforementionedreverse 'J pattern including horizontal leg 22 and vertical leg 25, itbeing understood that the contribution of the present invention is steelhead 21 at the periphery and that part of hardfacing 22 and 25immediately adjacent thereto, in particular the generally horizontalhardfacing 22 and portion of steel head 21. In this connection it shouldbe noted that the generally vertical portion of steel bead 2.1 andhardfacing 25 are desirable but not necessary to the practice of thepresent invention. So long as the horizontal portion are em ployed, anyof the aforementioned prior art methods of protecting ball plug weld 12are adequate.

Attention is invited to the fact that the hardfacing 22. and 25 of thedrawing extends radially somewhat beyond the outside surface of bit leg3. This permissable in drilling shallow holes used for seismograph work,blast holes, and the like, but is generally objectionable in deep holessuch as production-seeking oil well holes wherein it is often necessaryto lower a bit to the bottom of the hoie through the bore of a casing.For the latter type employment, it is apparent that the bit leg 3 may bedesigned and fabricated with an appropriate groove to receive metal bead21 and hardfacing 22. The deposit in such cases may be ground flush withthe outer surface of bit leg 3, as has been done with ball plug weld 12.

New Bit Example An example of using the present invention on a bit thirdon which no cone or hearing structure has been mounted and prior to heattreatment is:

A metal bead (ll) is laid down along the periphery of the bit leg 3using an atomic hydrogen torch and a inch diameter 3501 steel weldingrod and the backhand welding method to deposit a bead of about 3%;; inchthickness and A3 inch with. This rod has a weight percent composition ofSi=0.200.35 Ni=3.253.75 Mo=0.200.30 S=0.04 max. P=0.04 max. Balanceessentially Fe On subsequent heat treating of the assembled bit byfurnace soaking, oil quenching and tempering, it has a Rockwell Chardness of 25 to 35, although any greater hardness without loss oftoughness is desirable. The metal bead is applied to the lower edge ofthe bit leg surface and to the rising edge on the leading side of thebit leg, i.e., the side facing the direction of rotation.

Hardfacing 22 and 25 is then applied with the same atomic hydrogentorch, preferably by a tube application. One tube used successfully hasbeen designated 230 A and consists of a hollow steel tube filled withcast tungsten carbide particles. The wall of the tube is of low carbonsteel (0.15 w/o C. max), and the particulate carbide filling includessufficient ferromolybdcnum and ferromanganese powders (screened through80 mesh US. sieve) to make a binder of a composition of approximately 2weight percent (W/o), Mn, 0.5 w/ o Mo, balance low carbonsteel. The tubeis about /5 inch in outside diameter and has a wall thickness such thatthe binder is about 30 w/o of the combined weight of binder and tungstencarbide filler.

, The tungsten carbide particles in the tube are of the cast type,produced by reacting powders of tungsten and carbon in a graphitecrucible under high heat, and tapping the molten mixture into an oilbath. The quantities used, giving due regard to carbon pick-up from thecrucible, are preferably such as to produce a eutectic of WC and W Ccontaining about 4 w/o combined carbon. The relatively large particlesobtained from the oil bath are crushed and screened, in the presentexample to a size range of 14 to mils. V

The hmdfacing band or bead 22 and 25 thus deposited is of about ,1 inchthickness above surface 3 and varies in Width from inch to inch, thehorizontal portion 22 preferably being wider than vertical portion 25.There is no particular point for the upward termination of portion 2 5,and terminations co-extcnsive with weld plug 12 have provcn adequate.

Assembled Bi! Example In this procedure, the welder is working on a bitor bit third in which the bearing surfaces of the bit legs have alreadybeen heat treated and in which a cone 4 has been mounted on a bearingpin 5 with rollers 7 in place. Balls 8 have already been loaded throughopening 10 and bore 9, ball plug 11 has been added and fixed in place byweld 12.

It is necessary to observe special precautions to prevent overheating ofthe assembly, in particular the rollers and bearing surfaces. A coppershield is inserted between cone and bit leg, the cone or cones areimmersed in water throughout the process, and the bit head is cooled inwater between successive steps of depositing successive weld beads orportions thereof. The other precautions lie in the type welding torchand the materials used.

A metal bead 21 is deposited around the periphery of bit leg 3 using ashielded metal arc Welding method with a welding current of 100 to 110ampercs of direct current, the workpiece serving as the positiveelectrode. The welding electrode material may be of any of severalso-callcd air hardening" materials, two of which successfully employedin the present invention are Race and Airco 91. The first of these is aproduct of the Reed-Avery Company and has a typical deposit compositionby weight percent of 0.26 C, 1.17 Mn, 0.50 Si, 0.71 Ni, 2.15 Cr, balanceessentially Fe. The Airco 91 rod is a product of the Air ReductionCompany and has a typical deposit composition by weight percentage of0.33 C, 1.76 Mn, 0.10 Si, 2.80 Cr, balance essentially Fe. Each isdeposited from a Vs inch diameter electrode to form a bead about 7 inchhigh and W inch to M1 inch Wide, preferably with a cooling step betweendepositing the horizontal and vertical legs.

The same welding method is employed for depositing the hardfacing bands22 and 25, and the cgnsumable electrode used for the hardfacing issimilar to that used for hardfacing new bits above in that it consistsof a hollow tube filled with tungsten carbide particles, the tube wallagain being a low carbon steel. The tungsten carbide particles are of 20and 30 mesh U. S. Standard Sieve and comprise about w/o of the totalweight of binder plus hardfacing particles. Such rods or electrodes arecommercially available as the Stoody Companys Stoody Tube Borium and theVictor Equipment Companys Coated Victortube Electric welding rods.

In contrast with the preferred single ha-rdfacing head 22 of the new bittechnique above and as shown in the drawing, it is preferable in therework of assembled bits to apply hardfacing 2.2 (and 25) in two or morenarrow beads, each 1 to /2 inch wide by about inch high. This is done tominimize the heat which must be dissipated by the bit, and again has thepurpose of avoiding damage to the bearings. It is also highly desirableto pause and cool the bit between the depositing of bead segments andafter completing each head.

The complete hardfacing bands 22 and 25 may be laid down by thedescribed metal are technique, and indeed this technique is mostconvenient when the hardfacing is being applied in the field. When thebit is being factory reworked a final bead may be added above theelectric distance between the tip 14 of shirttail 13 and the line wherethe first atomic hydrogen head is to join the electric tube bead, about/2 inch. Substantially all of the vertical hardfacing portion 25 may bedeposited by the atomic hydrogen torch. The total width of all beads isabout /1 inch for the horizontal portion and /2 inch for the verticalportion.

Bits with shirttail hardfacing as in these examples have beenextensively field tested and have resulted in increases in footagedrilled averaging more than 70%. As one example, a number of bits withprior art hardfacing on the bit leg averaged 588 feet per bit before itwas necessary to pull them for loss of shirttail metal. At the samelocation and in the same formation, the same type and size bits with theshirttail hardfacing of the present invention drilled 1029 feet per bit,an increase of 75%.

While the present invention has been described in connection withrolling cone rock bits, it will be appreciated that it is notnecessarily limited thereto, but may be generally applied to structureshaving sharp corners subject to abrasion, e.g., other types of rockbits, reamers and the like. Broadly the invention comprises a structureon the outer surface of the rotating part consisting of a narrow bead ofa hard, tough metal at the edge of such surface immediately adjacent thesharp corner and a band of hardfacing material adjacent the metal beadin contact therewith. The metal bead should be of a minimum finalhardness of about 25 on the Rockwell C scale and may have any greaterhardness consistent With toughness. The hardfacing band may consist ofsintered or cast particles dispersed in a suitable binder, and may be ofother suitable hard particles as well as tungsten carbide.

In addition, while it has been indicated above that exposure to abrasiveconditions ordinarily produce no severe wear on shirttails and bit legsused in mud drilling, there are exceptions. The shirttail hardfacing ofthe present invention is equally applicable to earth penetrating toolsused in such mud drilling, including rock bits, reamers and shaftcutters, Le, a rolling cutter mounted on the bearing pin of a bit legwith a construction similar to that described above and with the samesharp corner at the tip of the shirttail.

What is claimed is:

1. A hardfacing structure on a member subject to abrasion on the outersurface thereof and terminating at a corner, such member having aportion at and adjacent such corner so relatively thin as to requirestrengthening prior to hardfacing but being otherwise relatively thick,such hardfacing structure comprising: a narrow head of a tough, hard,homogeneous metal alloy on said surface immediately adjacent said cornerand a substantially discrete band of hardfacing material on said surfaceimmediately adjacent said hard metal bead and in contact therewith, saidhardfacing material being a heterogeneous combination of wear resistantparticles in a tough alloy binder.

2. The hardfacing structure of claim 1 in which said hard metal is analloy steel having a minimum hardness of about 25 Rockwell C.

3. The hardfacing structure of claim 2 in which said hardfacing bandcomprises tungsten carbide particles in a binder of a low carbon steel.

4. The hardfacing structure of claim 3 in which said metal bead has awidth of about A; inch and said hardfacing band has a minimum Width ofabout inch.

5. A hardfacing structure on the shirttail and bit leg of a rock bit orother tool comprising a narrow bead ,of a tough, hard, homogeneous metalalloy welded on the outer surface of said shirttail immediately adjacentthe corner thereof and a band of hardfacing material welded on saidsurface above said metal bead and in contact therewith, said hardfacingmaterial being a heterogeneous combination of Wear resistant particlesin a tough alloy binder.

6. The hardfacing structure of claim 5 in which said metal bead has aminimum hardness of about 25 on the Rockwell C scale.

7'. The hardfacing structure of claim 6 in which said metal bead is anair hardening steel head.

8. A hardfacing structure for rock bit legs and shirttails and Welded tothe outer surfaces thereof including a narrow band of a tough hard metalextending generally horizontally across the tip of said shirttail andgenerally vertically along the leading edge of the periphery of saidshirttail and bit leg, and a hardfacing band similarly extendinghorizontally across said shirttail and vertically along said periphery,said hardfacing band being in supporting contact with said hard metalbead and extending vertically to the top of any ball plug Weld metal insaid bit leg, said hard metal bead being composed of a homogeneous alloysteel whereas said hardfacing bead is a heterogeneous combination oftungsten carbide particles dispersed in a steel binder.

9. The hardfacing structure of claim 8 in which said hard metal has aminimum hardness of about 25 Rockwell C.

References Cited by the Examiner UNITED STATES PATENTS 1,733,241 10/29Scott 175411 X 1,855,330 4/32 Zublin 175411 X 2,057,209 10/36 Schlurnpfl-4l1 X 2,086,682 7/37 Scott 175341 X FOREIGN PATENTS 1,244,3 9/60France.

CHARLES E. OCONNELL, Primary Examiner.

5. A HARDFACING STRUCTURE ON THE SHIRTTAIL AND BIT LEG OF A ROCK BIT OROTHER TOOL COMPRISING A NARROW BEAD OF A TOUGH, HARD, HOMOGENEOUS METALALLOY WELDED ON THE OUTER SURFACE OF SAID SHIRTTAIL IMMEDIATELY ADJACENTTHE CORNER THEREOF AND A BAND OF HARDFACING MATERIAL WELDED ON SAIDSURFACE ABOVE SAID METAL BEAD AND IN CONTACT THEREWITH, SAID HARDFACINGMATERIAL BEING A HETEROGENEOUS COMBINATION OF WEAR RESISTANT PARTICLESIN A TOUGH ALLOY BINDER.